Watershed is a land area that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, bays, and the ocean.
One change to the environment impacts everything around it. This is also true for the watersheds. Flint decided to make changes to their watershed and it changed the water just as the environment would change.
If they hadn't used a different water source, such as a river, they would've never had a problem and would have safe water.
Flints officials looked to see if they can save money if they switch to an alternative water source, which was Detroit water. A year later they switched to the Flint river. Residents starteded to complain about a smell and color of the new water. Later, companies detected in the water. Residents were urged to boil their water. Flint was found to be in violation of the Safe Drinking Water Act. Trihalomethanes were found in the water. Many other matters were at stake for Flint and still are.